Sleep Habits May Affect Brain Function

(Jul. 18, 2012) -- Too little or too much sleep may make your brain age more quickly, a new study says.

And another sleep study found that having sleep apnea may increase the risk for mild thinking problems or dementia.

The first study looked at data on more than 15,000 women in the Nurses' Health Study. Participants were followed for 14 years, beginning in middle age.

Researchers at Brigham and Women's Hospital in Boston found that people who slept five or fewer hours a day or nine or more hours a day had lower mental functioning than people who slept seven hours a day. Getting too little or too much sleep was the equivalent of aging mentally by two years, the researchers say.

Changing patterns

And women whose sleep patterns changed by two or more hours a day from middle age to later years also had worse mental functioning than women whose sleep patterns didn't change.

"We went in with the hypothesis that extreme changes in sleep duration might be worse for cognitive function because they disrupt the circadian rhythm, so these results line up nicely," says study author Elizabeth Devore, Sc.D.

Circadian rhythm refers to the physical, mental, and behavioral changes that occur in a 24-hour cycle.

Disrupted sleep

For the second study, researchers from the University of California, San Francisco, measured the sleep quality of more than 1,300 women older than 75. They found that participants with sleep apnea or other disordered sleep were more than twice as likely to develop mild cognitive impairment or dementia over five years than those without those conditions.

"Whether sleep changes, such as sleep apnea or disturbances, are signs of a decline to come or the cause of decline is something we don't know, but these studies ... shed further light that this is an area we need to look into more," says Heather Snyder, Ph.D., at the Alzheimer's Association, who was not involved in the studies.

The studies were two of four sleep studies presented this week at the Alzheimer's Association annual meeting in Vancouver. A third study looked at the effect of daytime sleepiness on mental functioning in old age, and the fourth found that sleep patterns were linked to levels of amyloid proteins in the brain. The proteins are linked to Alzheimer's disease.

Stages of Sleep

People once believed that sleep was simply a period of deep rest. Now researchers know that sleep is actually an active process for the brain. You spend about one third of your life asleep, but it's not wasted time. This is the time the body uses to repair and restore itself.

Here are the four basic stages of sleep:

Stage 1. The first stage of sleep is the lightest stage. At this point, your body processes slow down, and you may experience a sensation of falling. You begin drifting toward deeper stages of sleep. If awakened, which happens easily in this stage, you may remember images or waking dreams. Your arm, leg, or another part of your body may jump suddenly in this stage.

Stage 2. You spend about half of your slumber in this stage. Your eye movements stop and your brain waves slow down. If the electrical pulses that make up your brain waves were monitored, those watching might see slow waves known as theta waves and sudden bursts of activity, called sleep spindles. This is when bedroom temperature matters - a room that's either too warm or too cold can make it difficult to reach this stage of sleep.

Stage 3. Deeper into sleep, your brain waves slow profoundly into delta waves. You still may have sudden bursts of brain activity at this stage. Stages 3 and 4 are the stages in which your body and brain make all the repairs that help you get back on your feet after a tough day.

Stage 4. During this stage, slow delta brain waves become more prominent. This is your most restorative sleep, and it is much harder to awaken from this stage than from stage 1. In fact, you could be extremely disoriented if this were to happen. Sleepwalking and sleep talking are most common in this stage. During stages 3 and 4, your body also releases hormones crucial to growth and development.

Always talk with your health care provider to find out more information.

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